In the title compound, [Mg(C(44)H(28)N(4))(H(2)O)(2)]·C(12)H(24)O(6), the Mg(II) cation lies on an inversion center and is octa-hedrally coordinated by the four N atoms of the deprotonated tetra-phenyl-porphyrin (TPP) ligand and by two water mol-ecules. The asymmetric unit contains one half of the [Mg(TPP)(H(2)O)(2)] complex and one half of an 18-crown-6 mol-ecule. The average equatorial magnesium-pyrrole N atom distance (Mg-N(p)) is 2.071 (1) Å and the axial Mg-O(H(2)O) bond length is 2.213 (1) Å. The crystal packing is stabilized by two O-H⋯O hydrogen bonds between coordinating water mol-ecules and adjacent 18-crown-6 mol-ecules, and exhibits a one-dimensional supramolecular structure along the a axis. The supramolecular architecture is futher stabilized by weak C-H⋯π inter-actions. The 18-crown-6 mol-ecule is disordered over two sets of sites with an occupancy ratio of 0.8:0.2.